The present invention relates to a control valve used in a variable displacement compressor, more specifically, to control valve that adjusts the pressure in a crank chamber to control the displacement of a compressor.
In a typical variable displacement compressor, the inclination angle of a swash plate varies according to the pressure in a crank chamber (crank pressure) to change the displacement of the compressor. There are two methods to control the crank pressure: the inlet control method and the outlet control method. The inlet control method is a method in which gas is constantly released from the crank chamber to a compressor suction chamber at a fixed flow rate, and the flow rate of gas drawn into the crank chamber from a compressor discharge chamber is adjusted to control the crank pressure. The outlet control method is a method in which highly pressurized gas is constantly supplied to the crank chamber at a fixed flow rate, and the flow rate of gas released from the crank chamber to the discharge chamber is adjusted to control the crank pressure.
The inlet control method permits the crank pressure to quickly increase, which improves the response of the compressor. However, to maintain the crank pressure, the flow rate of highly pressurized gas flowing into the crank chamber must correspond to that of gas flowing out of the crank chamber. In other words, a relatively great amount of highly pressurized gas is required to maintain the crank pressure. The outlet control method, on the other hand, is advantageous in that little highly pressurized gas is required to maintain the crank pressure. However, the outlet control method cannot quickly increase the crank pressure and therefore does not improve the compressor response. Therefore, a compound control valve, which has the advantages of both inlet and outlet control mechanisms, has been introduced. For example, Japanese Unexamined Patent Publication No. 5-99136 discloses such a compound control valve.
The control valve disclosed in the publication has a first valve body and a substantially annular second valve body. The first valve body selectively opens and closes a supply passage, which connects a discharge chamber to a crank chamber. The second valve body selectively opens and closes a bleed passage, which connects the crank chamber to a suction chamber. The first and second valve bodies are actuated by a common transmission rod. The rod is electromagnetically moved by a solenoid to actuate the valve bodies. The solenoid urges the rod by a force that corresponds to the value of a supplied current. The rod slidably extends through the second valve body. The control valve also includes a diaphragm. The diaphragm actuates the second valve body according to the suction pressure of the compressor.
The first valve body and the second valve body are not actuated at the same time. That is, the first valve hole and the second valve hole are not opened at the same time. During a normal displacement control procedure, the diaphragm receives the force of the solenoid through the rod and actuates the second valve body in accordance with the suction pressure to adjust the opening degree of the bleed passage. In this state, the first valve body closes the supply passage. However, when the compressor displacement needs to be quickly decreased, the value of current supplied to the solenoid is maximized to maximize the force of the solenoid. This causes the second valve body to close the bleed passage and permits the rod to move the first valve body to open the supply passage. As a result, the crank pressure quickly increases, which quickly decreases the compressor displacement.
In the field of variable displacement compressors for vehicles, clutchless compressors are becoming standard. A clutchless compressor is directly coupled to a vehicle engine. Clutchless compressors are advantageous in reducing weight and cost.
When a compressor is operating, gas circulates within the compressor. Atomized oil in the gas lubricates the moving parts of the compressor. A compressor with a clutch can be disconnected from the engine by disengaging the clutch when refrigeration is not needed. The compressor is stopped accordingly. In this state, the moving parts of the compressor require no lubrication.
A clutchless compressor continues operating as long as the engine runs even if refrigeration is not needed. When refrigerant is not needed, the compressor is operated at the minimum displacement to reduce the load on the engine. During the minimum displacement operation, the moving parts must be lubricated. Therefore, a compressor in which gas circulates during the minimum displacement operation has been proposed. Such a compressor has a gas circuit, in which gas circulates through a discharge chamber, a crank chamber, a suction chamber, cylinder bores and a discharge chamber.
Publication No. 5-99136 discloses a control valve used in a compressor having a clutch. If the control valve of the publication is used in a clutchless compressor, gas cannot be circulated in the compressor during the minimum displacement operation. That is, when the compressor is operating at the minimum displacement, the second valve body closes the bleed passage and the first valve body opens the supply passage. Therefore, although gas flow from the discharge chamber to the crank chamber through the supply passage is permitted, gas does not flow from the crank chamber to the suction chamber through the bleed passage. Thus, a gas circuit is not formed within the compressor. The second valve body may temporarily open the bleed passage in accordance with a change of the suction pressure. However, the first and second valve bodies do not simultaneously open. Thus, gas only occasionally circulates within the compressor.
An auxiliary passage, which is independent from the bleed passage in which the control valve is located, may be formed in the compressor housing to connect the crank chamber to the suction chamber. The auxiliary passage would permit gas to circulate within the compressor during the minimum displacement operation. However, the auxiliary passage would undermine one of the advantages of the control valve of the publication. That is, the auxiliary passage limits the ability to quickly increase the pressure of the crank chamber. Also, forming the auxiliary passage complicates the manufacture.
Accordingly, it is an objective of the present invention to provide a displacement control valve that includes an inlet valve mechanism and an outlet valve mechanism and easily forms a gas circuit within a compressor.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve for a variable displacement compressor is provided. The displacement of the compressor varies in accordance with the pressure in a crank chamber. The compressor includes a suction pressure zone, the pressure of which is a suction pressure, a discharge pressure zone, the pressure of which is a discharge pressure, a bleed passage for releasing gas from the crank chamber to the suction pressure zone, and a supply passage for supplying gas from the discharge pressure zone to the crank chamber. The control valve includes an outlet valve mechanism, an inlet valve mechanism, a transmission member, an electromagnetic actuator and a communication passage. The outlet valve mechanism is located in the bleed passage to adjust the opening degree of the bleed passage. The inlet valve mechanism is located in the supply passage to adjust the opening degree of the supply passage. The transmission member extends between the outlet valve mechanism and the inlet valve mechanism to couple the outlet valve mechanism with the inlet valve mechanism. The transmission member moves axially. When the inlet valve mechanism is in an open state, the outlet valve mechanism is in a closed state. The electromagnetic actuator axially urges the transmission member by a force, the magnitude of which corresponds to the value of a current supplied to the actuator. The communication passage is formed in the outlet valve mechanism. When the outlet valve mechanism is in the closed state, the communication passage may be opened, depending on the axial position of the transmission member, for communicating the crank chamber with the suction pressure zone.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.